I need to find out how much sugar I will need when I only have 2 cups of flour instead of the normal 3 cups of flour.

Amount of sugar 2 cups, amount of flour 3 cups, this means that for every cup of flour you will need 2/3 of cup of sugar. if you have only 2 cups of flour you will need (2/3)*2 cups of sugar = 4/3 0r 1 cup and 1/3 more.